8

FN7333.6

October 9, 2007

Applications Information

The EL7516 is a high frequency, high efficiency boost

regulator operated at constant frequency PWM mode. The

boost converter stores energy from an input voltage source

and delivers it to a higher output voltage. The input voltage

range is 2.5V to 5.5V and the output voltage range is 5V to

18V. The switching frequency is selectable between 600KHz

and 1.2MHz, allowing smaller inductors and faster transient

response. An external compensation pin gives the user

greater flexibility in setting output transient response and

tighter load regulation. The converter soft-start characteristic

pin allows the user to completely shut-down the device.

Boost Converter Operations

Figure 28 shows a boost converter with all the key

components. In steady state operating and continuous

conduction mode where the inductor current is continuous,

the boost converter operates in two cycles. During the first

cycle, as shown in Figure 29, the internal power FET turns

on and the Schottky diode is reverse biased and cuts off the

current flow to the output. The output current is supplied

from the output capacitor. The voltage across the inductor is

is the inductance. The inductance is magnetized and energy

is stored in the inductor. The change in inductor current is:

FIGURE 25. TRANSIENT RESPONSE - 1.2MHz

FIGURE 27. PACKAGE POWER DISSIPATION vs AMBIENT

TEMPERATURE

FIGURE 28. PACKAGE POWER DISSIPATION vs AMBIENT

TEMPERATURE

0.1ms/DIV

200mV/DIV

0

1

2

3

4

5

3

3.5

4

4.5

5

5.5

6

SHDN TURN OFF

SHDN TURN ON

JEDEC JESD51-7 HIGH EFFECTIVE THERMAL

CONDUCTIVITY TEST BOARD

1.0

0.9

0.6

0.4

0.3

0.2

0.1

0

0

255075

100

125

AMBIENT TEMPERATURE (°C)

85

870mW

θ

11

5°C

/W

M

SO

P8

0.8

0.5

0.7

JEDEC JESD51-3 LOW EFFECTIVE THERMAL

CONDUCTIVITY TEST BOARD

0.6

0.4

0.3

0.2

0.1

0

0

255075

100

125

AMBIENT TEMPERATURE (°C)

85

486mW

θ

20

6°C

/W

M

SO

P8

0.5

ΔI

L1

Δt1

V

IN

L

---------

×

=

Δt1

D

f

SW

----------

=

D

Duty Cycle

=

ΔV

O

I

OUT

C

OUT

----------------

Δt

1

×

=

(EQ. 1)

EL7516